02/08/2011

How Diet Affects Cancer

Written by Dr. Keith I. Block, MD

Diet affects cancer both directly and indirectly. Nutrients directly impact the mechanisms by which cancer cells grow and spread. They indirectly help control the cancer by changing the surrounding biochemical conditions that either encourage or discourage the progression of malignant disease. The bottom line is that what you eat can spell the difference between conquering your disease and having it rage out of control.

Here are some examples of findings from recent studies that support the importance of diet in fighting cancer:

Diets high in fat and refined carbohydrates make you more likely to become overweight, which in turn increases your risk of tumor recurrences. Obese men are at significantly greater risk of developing more aggressive prostate cancer.

Dietary fats can impair the body's anti-cancer defenses by depressing the activity of natural killer (NK) cells, while a low-fat diet markedly increases NK activity. Natural killer cells play a key role in preventing metastasis.

Obese breast cancer patients are two to four times more likely to experience a recurrence than women of normal weight.

For every additional 10 percentage points of calories derived from fat in the diet of newly diagnosed breast cancer patients -- by going from 25 percent to 35 percent of calories from fat -- the risk of recurrence approximately doubles. An increase of 10 percentage points is alarmingly easy: just add 4 ounces of beef, 4 ounces of mozzarella cheese (about the size of three 9-volt batteries), a cup of ice cream, or four pats of butter to your daily intake and you're there.

High intake of many dietary fats is linked with higher rates of cancer recurrence, lower rates of survival, or both. At the American Society of Clinical Oncology meeting in 2005, I listened to a stunning presentation of a randomized controlled study of 2,400 breast cancer patients. It found that those who adopted a diet in which 20 percent of the calories came from fat (the U.S. norm is more like 35 percent) had a 24 percent lower rate of relapse. The lowered risk of relapse was particularly great for the 42 percent of women with the more dangerous estrogen-receptor-negative breast cancers. Because these women have fewer good conventional options, this is an especially important finding.

Despite this overwhelming evidence for the benefits of a healthy diet when you are fighting cancer, that is not what mainstream medicine recommends. Yes, when it comes to cancer prevention, the American Cancer Society recommends a diet that is heavy on fruits, vegetables, whole grains, and low-fat proteins while restricting unhealthy fats, refined carbs, and fatty red meats. So far, so good. Yet the standard advice for patients with cancer -- that is, those for whom prevention didn't work -- is "all you can eat." Cancer patients are told to get all the calories they can, from butter, margarine, high-fat dairy products, mayonnaise, eggs, meat, hard and soft cheese, ice cream, and peanut butter. The rationale is that a fat- and calorie-packed diet prevents or combats cachexia, the "starvation response" seen in cancer patients. It does not. But this response is hardly universal; only some patients become cachectic, and only at certain points in their treatment. The reality is that there are far more patients for whom "all you can eat" is exactly the wrong prescription: it makes them fill their plates with animal protein, saturated fats, unhealthful omega-6 fats, and refined carbohydrates, all of which have tumor-promoting properties. In fact, a 2007 study reported in the Journal of the American Medical Association found that stage III colon cancer patients who ate the least meat, fat, refined grains, and desserts had half the mortality risk of those who ate the most of these foods.

I don't want to pick on mainstream cancer groups -- in my five years as vice president of the uptown Chicago chapter of the American Cancer Society (ACS), I saw firsthand the good intentions of everyone involved. Nonetheless, the disconnect between the ACS's cancer-prevention dietary advice and its cancer-fighting dietary advice is hard to justify. Even laypeople can see that. A number of my patients have said to me, "My doctor used to advise that I should eat fruits and vegetables and avoid too much meat and fat so I wouldn't get cancer. Now that I got a diagnosis of cancer, I'm supposed to eat cheesecake, milk shakes, and cream sauce. That doesn't make sense." They're right: it strains credulity to think that the very foods you are told to minimize in order to reduce your risk of developing cancer should be dietary staples once you have cancer. The cheesecake-and-cream-sauce advice also ignores the growing scientific evidence of the tumor-promoting potential of the standard American diet. To a great extent, the foods recommended for cancer prevention are also the foods that seem to suppress cancer after it's diagnosed. In most cases it is reasonable to use prevention studies as a guide for how patients should eat, especially in cancers where healthy diets reduce risk.

Comments

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Hello,

Do you have any suggestions for people who've had colostomies or ileostomies or colon resections that leave them seemingly unable to tolerate much in the way of fresh fruits and vegetables?

I have been very lucky with the resection I had, as my body seems to prefer raw fruits, veggies, nuts & seeds... everything works fine, and for that I am quite grateful.

However, I know a few people with ostomies, resections or other diversions who end up eating a lot of white-floury products and other things that offer little nutrition, and few vegetables, simply because their systems are altered and that's all that seems to go through okay.

Generally I have found that estrogen contents in foods are less
than in herbs. My suggestion for women with hormone imbalance is to
avoid herbs which have estrogenic activities such as Don Quei,
Licorice, Ginseng, Royal Jelly, fennel, hops, anise, clover, flax
seed oil and evening primrose oil even though they may make you
feel better initially. Estrogen-containing foods such as alfalfa,
chick pea, carrot (or beta carotene) can be taken occasionally but
not on a regular basis.